Steam Now Allows Users to Cancel and Refund Pre-Orders on Their Own
To ease the pain of buyer's remorse, Steam has implemented a self-use "Refund This Item" mechanism for any pre-order game that has yet to be released. This automatic system will remove the pre-order game from the Steam Library regardless of payment method and credit their Steam Wallet appropriately. Unfortunately, this means that users wanting a full refund will still have to contact Steam Support. That may be problematic to some as it may not be worth the effort to go through the extra steps for the full refund. However, Steam offers over 3,000 games and is steadily adding games daily, so finding a game to purchase should not be difficult.
Source: Steam Forums